The great expansion of data communications, and the increases in the bandwidth of communications and control purposes, has led to increased use of optical signal paths for carrying wide-bandwidth optical systems. A particular problem with optical control systems is that of switching light signals flowing in a light path, as for example switching the light path ON or OFF as to a receiving device, or of switching light flowing along a signal path among two or more signal paths.
The prior art contains many mechanically operated switches, such as those which physically move a mirror on a flexible mirror support into an optical path between aligned, collimated optical fibers, to thereby couple the light to either a first or a second output optical fiber, or which move the end of an optical fiber between a first position in which it couples light into an output optical fiber and a second position in which light is not so coupled. Such mechanical switches often require close mechanical tolerances, and may be expensive for that reason. Mechanical switches also tend to have reliability problems attributable to such factors as fatigue of the moving member resulting from repeated flexing, and from misalignment due to shock and vibration, and also tend to have limited operating or switching speed resulting from mechanical inertia.
Other optical switches are nonmechanical, but are more complex than might be desired, due to the use of switching devices which are polarization-sensitive. If the light being switched is unpolarized, a polarization-sensitive switch will switch only the preferred polarization, with the result that the non-preferred polarization is not switched. This, in turn, results in a 3-dB loss in the switch as to the switched signal, and may result in poor isolation as a result of the large amount of signal power remaining in the switched channel. This polarization sensitivity can be corrected, as, for example, in U.S. Pat. No. 4,913,509, by separately processing the two different polarizations, but this results in added complexity.
Improved nonpolarized optical switches are desired.